Being low on energy during the day might be caused by trouble breathing while you sleep, even if you don't actually feel sleepy, a new University of Michigan study suggests. In fact, doctors and patients may be missing the real cause of some cases of daytime fatigue and lack of energy: a potentially serious but treatable condition known as sleep apnea.

The finding, in the August issue of Chest, demonstrates that patients with undiagnosed sleep apnea don't always describe their symptoms using the term -- sleepiness -- that doctors are currently trained to listen for. In effect, the words that patients use may get in the way of the doctor's initial diagnosis. But, the paper says, if patients who are fatigued but not sleepy have laboratory sleep tests, they may show the interrupted breathing patterns of sleep apnea.

"Sleep apnea is a common and underdiagnosed condition in which breathing stops temporarily dozens or even hundreds of times a night. It can have an important impact on a person's productivity, quality of life and health if not treated," says Ronald Chervin, M.D., M.S., assistant professor of neurology.

Many people suffer from interrupted sleep and do not even realize it. But interrupted sleep can cause as many health problems as not enough sleep. Jacob Teitelbaum is a firm believer in the importance of sleep if you suffer from CFS or FM.

“Breaking the cycle of poor sleep and maintaining quality sleep for six to nine months is critical to breaking the cycle of FM, CFS, and severe fatigue,” says Teitelbaum.

"It is important to note that growth hormone released during stages three and four of sleep is responsible for many of the repair processes that go on in our muscles and in the rest of our body. It is theorized that this loss of repair function that normally occurs during deep sleep contributes to the pain of FM. Several studies have now shown that if you wake up people whenever they go into deep sleep, or even lightly shake them so they go from deep sleep into light sleep, they will develop classic FM-like pain within one to two weeks and often within one night.”

The study points out how important it is for physicians to listen carefully to how patients describe their problems. In fact, Chervin made the finding by "listening" to patients - both their words and their sleep patterns. He reviewed survey answers and sleep test results from 190 people who had been referred by their regular physicians for sleep studies at the U-M's Michael S. Aldrich Sleep Disorders Laboratory, where Chervin is director.

The subjects or their physicians suspected a sleep disorder, so these individuals don't represent the general population. But the results from their sleep tests, and their answers to questions about how they felt, yield surprising trends that may be important to doctors and the many Americans who haven't yet sought help for problems with getting a good night's sleep.

In all, 73 percent of the study's subjects said they suffered from sleepiness, fatigue, tiredness or lack of energy often or almost all the time. But when the four descriptive terms were compared independently, less than half the patients reported feeling sleepy often or always, while 62 percent said they lacked energy often or always, 57 percent reported problems with fatigue, and 61 percent said they felt tired. Women were more likely to describe such symptoms.

Asked which of the symptoms was most significant to them, more patients chose "lack of energy" than any other problem, and almost twice as many chose it than chose "sleepiness." Chervin and his colleagues also asked subjects which symptom most kept them from accomplishing what they wanted to do during the day. Forty-four percent said lack of energy, while only 16 percent said sleepiness.

Women in the study reported all four symptoms more than men did. They were four times as likely to say they had a lack of energy, and three times as likely to state they felt tired during the day. Chervin theorizes that men may be culturally less willing to admit any of the problems asked about in the survey. Only when told they had to choose one of the symptoms did the men show similar rates of complaint as women. But, Chervin adds, there may be some neurophysiological differences in the way men and women perceive the effects of poor sleep.

"These results suggest that patients who deny being sleepy may not be as unlikely to have sleep apnea as is sometimes assumed," Chervin says. "We need more research, in the broader population, on relationships between symptoms patients report and the results sleep tests."

The most common form of the disease is called obstructive sleep apnea, in which the upper airway in the throat becomes obstructed. Breathing stops or diminishes for periods of 10 seconds to a minute or more. Often, apnea is worsened by excessive weight, having oversized tonsils, or having other structural or neurological problems in the upper airway. There is growing evidence that it may cause numerous medical conditions such as high blood pressure, heart attack, heart arrhythmia, stroke, and cognitive problems.